1. Field of the Invention
The present invention relates to a thrust bearing assembly of a kind generally used in machines and automobile transmissions, and also to a roller retainer used therein.
2. Description of the Prior Art
In order to avoid an accidental separation of rollers and also to facilitate handling, a thrust needle roller bearing assembly of a shell type has been suggested, in which a pair of raceway members and a roller retainer are assembled non-separably together into a trinitarian unitary structure. One example of this type of the bearing assembly is shown in FIGS. 7A to 8.
Referring to FIGS. 7A to 8, the bearing assembly shown therein comprises a pair of annular raceway members 51 and 52, a plurality of rolling elements 54 and a retainer 53 carrying the rolling elements 54 and interposed between the raceway members 51 and 52. The raceway member 51 which serves as an inner race, has an inner peripheral edge formed with a collar 51a whereas the raceway member 52 which serves as an outer race has an outer peripheral edge formed with a collar 52a. The collars 51a and 52a have respective retaining pawls 55 and 56 formed integrally therewith to keep the roller retainer 53 in a fashion non-separable from the space delimited between the raceway members 51 and 53. The roller retainer 53 is shaped from a thin plate by the use of a press work so as to have a generally W-shaped cross-section having hill portions and a dale portion between the hill portions and has generally rectangular pockets 57 defined therein in a number equal to the number of the rolling elements 54. The hill and dale portions of the roller retainer 53 are formed with roller retaining pawls 58 and 59 so as to protrude a slight distance into the associated pocket 57.
The thrust roller bearing assembly of the trinitarian unitary structure has been found problematic in that depending on the manner of use, the thrust roller bearing assembly would be intermittently subjected to the load by which the roller retainer 53 may be clamped in a radial direction between the respective collars 51a and 51b of the raceway members 51 and 52. Accordingly, if the roller retainer 53 is prepared from the thin plate by the use of the press work such as shown, an attempt to manufacture the thrust roller bearing assembly in a compact size would result in lack of a sufficient physical strength.
By way of example, the thrust roller bearing assembly shown therein is often used in and disposed between a sun gear and a planetary gear in a planetary gear assembly generally used in an automobile transmission. A result of analysis of the behavior of the thrust roller bearing assembly used in the automobile transmission has shown that because during the gear shifting operation the roller retainer 53 had been clamped in a radial direction between the respective collars 51a and 51b of the raceway members 51 and 52 under the influence of the centering action between the raceway members 51 and 52 and because the radial load had therefore repeatedly acted on the roller retainer 53 each time the gear shifting position was changed, a relatively high risk has been shown that the roller retainer 53 lacked a sufficient physical strength. For this reason, demand has been made to increase the physical strength of the roller retainer 53 by means of, for example, using a relatively thick plate as material therefor.
On the other hand, in order to cope with the attempt to compactize the automobile transmission (particularly, the automatic transmission for automobile use) and to permit the automobile transmission to withstand the high load, the bearing assembly has come to be designed within severe dimensional limits, particularly reduction in section. In other words, the use of rolling elements of a reduced size is desired for and, in order to accomplish this in the generally W-shaped roller retainer 53 such as shown in FIGS. 7A to 8, there is no way other than to reduce the thickness of the plate for the roller retainer 53 accompanied by the reduction of the roller retainer 53 and also to increase the number of the rolling elements used with reduction in width of the column between the neighboring pockets 57 in the roller retainer 53.